The tumor blood vessel is the passage for tumor cells to obtain nutritional substances and remove metabolites as well as one of the key ways for tumor cells to escape and transfer, and its morphology and function are different from those of the normal blood vessel system of organism, thus, it is one of the key targets for tumor targeted therapy. The targeted therapy of tumor blood vessel mainly includes two modes of inhibiting generation of new-born blood vessels and blocking the existing tumor blood vessels, wherein the therapy of blocking the existing blood vessel treats the tumor by selectively damaging the existing tumor blood vessels, cutting off tumor blood supplying and inducing the tumor cell to generate ischemic necrosis. Therefore, how to specifically block the blood vessel of the tumor part without influencing the normal tissue blood vessel of organism becomes the hotspot of study.
Tissue factor (TF) is a transmembrane glycoprotein with molecular weight about 47 kDa, and it plays an important role for thrombopoiesis. Normally, TF is in the adventitial cells of vascular wall but not in circulation or doesn't contact the circulation blood. When the completeness of vascular wall is damaged, TF is exposed in the circulation blood, and activates coagulation cascade activation to display the hemostatic effect. TF consists of 263 amino acid residues, wherein 219 amino acid residues of the amino terminal are outside the cell membrane which is the active part of TF. It's proven by study that, when this part is in the free state, no coagulation activity exists, but when this part is anchored on the cell membrane and exposed in blood, the coagulation activity similar as the full-length factor generates, thus, the sequence of this part is called as the truncated tissue factor (tTF). In view of this characteristic, if molecule having tumor targeting function specially anchors tTF in tumor tissue, thrombopoiesis will be arisen in tumor blood specially, so as to cut off tumor blood supplying and metabolite removing pathway, accordingly to achieve the goal of treating tumor.
Tumor targeted molecule pHLIP is a polypeptide consisting of 35 amino acids. When circulating in body (pH=7.35-7.45), the tumor targeted molecule pHLIP is in the free extension state, but cannot be anchored in the specific tissue. When it reaches the tumor part (pH<7), the conformational change of acid response is generated to form α-helix structure, and the interactive action with cell membrane is also generated, then, the tumor targeted molecule pHLIP is inserted into cell membrane to be anchored in endothelial cell surface.
If above truncated tissue factor tTF and the tumor targeting molecule pHLIP are recombined into the fusion protein so as to ensure their respective functions not be influenced by each other. The fusion protein can be positioned to surface of endothelial cells of the tumor blood vessel by pHLIP, and display the coagulation function of tTF in the tumor blood vessel to generate thrombus, so as to block the blood supply for the tumor part and to achieve the goal of treating tumor, which has important significance for tumor treatment.